1. Field of the Invention
This invention relates generally to optical disks. More particularly, it relates to a technique and method for achieving higher density data storage in an optical disk such as a compact disk (CD) or digital video disk (DVD).
2. Background of Related Art
Conventional optical disk players (e.g., a CD ROM player, music CD player, DVD player, etc.) contain data bits within pits and/or bumps formed along tracks in the surface of one side of an optical disk (e.g., a compact disk (CD) or digital video disk (DVD). In these conventional systems, the traveling distance of a laser beam is changed in accordance with a the presence or absence of a pit in certain technologies, and/or the presence of a bump using other technologies.
FIG. 7 shows a cross sectional view of a conventional optical disk 740 containing a series of pits 702, 704, 706, 708 along a track path.
In particular, in FIG. 7, a plurality of pits 702-708 are presented one-by-one to a focal point of a laser beam. The laser 700 outputs a particular laser beam, e.g., 780 nm laser beam, and senses the distance to a reflection point of the laser beam upon its return back to the laser 700. If the pit 702-708 is a deep pit, e.g., as shown in pits 702, 704 and 708, the data point is determined to be of a particular logic level (e.g., a logic xe2x80x980xe2x80x99). Conversely, if the pit is either non-existent at a data point, or of another depth, as shown in pit 706, the data point is determined to be of the opposite logic level (e.g., a logic xe2x80x981xe2x80x99).
FIG. 8 shows the bit density in a conventional optical disk, wherein each pit represents a single bit.
More recently, advances have been made in an attempt to increase the density of an optical disk. For instance, more advanced techniques use a variably adjustable depth of a pit or height of a bump to represent a plurality of bits in a digitally encoded signal.
As examples, U.S. Pat. No. 5,724,339 to Ogawa discloses the use of pits having a cross-sectional shape viewed from a direction perpendicular to the laser, selected from at least two different shapes. The different cross-sectional shapes are determined based on an amount of reflected light. U.S. Pat. No. 5,359,591 to Nomoto similarly discloses the use of pits having different cross-sectional shapes, as does U.S. Pat. No. 5,572,508 to Satoh et al. U.S. Pat. No. 5,559,787 uses polarization of reflected light depending upon the depth of the pit to increase data bit density in each pit. U.S. Pat. No. 5,471,455 to Jabr provides a track with a continuous pit having variable depth surface steps, and U.S. Pat. No. 5,577,016 to Inagaki et al. discloses changing the wavelength of a laser depending upon the depth of measured pits.
Unfortunately, the use of different cross-sectional pit shapes with respect to the laser beam, and/or the use of variable-depth pits, requires a complicated laser system which is not only capable of determining whether or not a reflection has been detected from a particular data point, but also which must distinguish between slight differences in reflective qualities.
Other patents, such as U.S. Pat. No. 5,995,481 to Mecca control the depth of pits and/or bumps to be equal to one-half the wavelength of the laser light. General improvements in the quality of reflective properties of pits were disclosed in U.S. Pat. No. 5,696,758 to Yanagimachi et al. U.S. Pat. No. 5,357,499 to Nomoto discloses angling of the bottom of single-bit pits toward the laser.
While these patents disclose improvements which might improve the reliability of reading each pit as a bit, they do not provide a significant increase in the data density of an optical disk.
There is a need for a technique and apparatus for increasing the density of an optical disk without requiring complicated reflection level sensitivity in a laser system otherwise required to measure multiple levels of reflection of a laser beam.
In accordance with the principles of the present invention, an optical disk comprises a plurality of multi-faceted pits forming a data track. Each multi-faceted pit includes a plurality of facets. Each of the plurality of facets are encoded with a data bit by an angling of the facet with respect to a surface of the optical disk.
An optical disk reading system in accordance with another aspect of the present invention comprises a first laser to present a laser beam to a first facet of each of a plurality of multi-faceted pits of a data track formed in the optical disk. A second laser presents a laser beam to a second facet of each of the plurality of multi-faceted pits of the data track.
An optical disk reading system in accordance with yet another aspect of the present invention comprises a laser having at least two reading positions. A first reading position of the laser presents a laser beam to a first facet of each of a plurality of multi-faceted pits of a data track formed in the optical disk. A second reading position of the laser presents the laser beam to a second facet of each of the plurality of multi-faceted pits of the data track.
An optical disk in accordance with still another aspect of the present invention comprises a plurality of multi-faceted bumps forming a data track. Each multi-faceted bump includes a plurality of facets. Each of the plurality of facets are encoded with a data bit by an angling of the facet with respect to a surface of the optical disk.
A method of reading separate data streams from an optical disk in accordance with still another aspect of the present invention comprises positioning a laser beam to read a status of a first facet of each of a plurality of pits in a track of the optical disk. The laser beam is repositioned to read a status of a second facet of each of the plurality of pits.
A method of reading separate data streams from an optical disk of another aspect reflects a first laser beam from a first facet of each of a plurality of pits in a track of the optical disk to read a first stream of data bits from the plurality of pits. A second laser beam is reflected from a second facet of each of the plurality of pits to read a second stream of data from the plurality of pits.